What Is Achondroplasia?
What is Achondroplasia?
Commonly known as dwarfism. It is the most common type of short-limbed disproportionate dwarfism. The term achondroplasia was first used by Parrot in 1878. Although the term ‘achondroplasia’ literally means ‘without cartilage’, but in achondroplasia, the cartilage is formed but it does not get converted to bone especially, in the limbs. People with achondroplasia have short arms and legs, normal size trunk and a large head.
Another condition similar to achondroplasia is hypochondroplasia but the symptoms tend to be more severe in achondroplasia.
What causes achondroplasia?
It is a rare genetic disorder which gets transmitted as autosomal dominant trait. This means that one copy of altered gene in each cell is enough to cause the disease.
Chromosomes are found …show more content…
in the nucleus of all body cells. They carry the genetic characteristics of each individual. Pairs of human chromosomes are numbered from 1 through 22 (autosomal chromosomes), with an unequal 23rd pair (sex chromosomes), of X and Y chromosomes for males and two X chromosomes for females. Each chromosome has a short arm designated as “p” and a long arm identified by the letter “q.” Chromosomes are further subdivided into bands that are numbered.
Human traits, are a result of the interaction of two genes, one received from the father and one from the mother. Autosomal dominant disorders are due to defective genes in autosomal chromosomes. Since they are dominant, only one copy of defective gene, coming from either the mother or the father, is sufficient to cause the disease.
Achondroplasia is due to the mutations of a gene known as “fibroblast growth factor receptor-3” (FGFR3). The FGFR3 gene is located on the short arm (p) of chromosome 4 (4p16.3). The FGFR3 gene provides instructions for making a protein that is involved in the development and maintenance of bone tissue. Two specific mutations in the FGFR3 gene are responsible for almost all cases of achondroplasia. These mutations cause the FGFR3 protein to be overly active, which interferes with skeletal development and leads to the disturbances in bone growth seen with this disorder.
About 80 percent of the cases are due to new mutations in the FGFR3 gene.
These are random mutations. They have normal sized parents and there is no family history of dwarfism. The remaining cases, have inherited an altered FGFR3 gene from one or two affected parents. Individuals who inherit two altered copies of this gene have a severe form of achondroplasia that causes extreme shortening of the bones and an underdeveloped rib cage. These cases are usually still birth or die soon after birth due to respiratory failure.
When both parents have achondroplasia, 75% of their offspring is affected, of which, 25% are homozygous i.e. they have two copies of the gene (which is ordinarily fatal in the first few months of life), 50% is heterozygous (have only one copy of gene), and 25% are unaffected. When one parent has achondroplasia, the chance of transmitting this gene to each child is 50%.
How common is Achondroplasia?
Achondroplasia appears to affect males and females in equal numbers. All races are affected equally. About 10,000 individuals have achondroplasia in the United States. Worldwide, achondroplasia is the most common skeletal dysplasia, affecting about 1 in every 40,000
children.
Commonly known as dwarfism. It is the most common type of short-limbed disproportionate dwarfism. The term achondroplasia was first used by Parrot in 1878. Although the term ‘achondroplasia’ literally means ‘without cartilage’, but in achondroplasia, the cartilage is formed but it does not get converted to bone especially, in the limbs. People with achondroplasia have short arms and legs, normal size trunk and a large head.
Another condition similar to achondroplasia is hypochondroplasia but the symptoms tend to be more severe in achondroplasia.
What causes achondroplasia?
It is a rare genetic disorder which gets transmitted as autosomal dominant trait. This means that one copy of altered gene in each cell is enough to cause the disease.
Chromosomes are found …show more content…
in the nucleus of all body cells. They carry the genetic characteristics of each individual. Pairs of human chromosomes are numbered from 1 through 22 (autosomal chromosomes), with an unequal 23rd pair (sex chromosomes), of X and Y chromosomes for males and two X chromosomes for females. Each chromosome has a short arm designated as “p” and a long arm identified by the letter “q.” Chromosomes are further subdivided into bands that are numbered.
Human traits, are a result of the interaction of two genes, one received from the father and one from the mother. Autosomal dominant disorders are due to defective genes in autosomal chromosomes. Since they are dominant, only one copy of defective gene, coming from either the mother or the father, is sufficient to cause the disease.
Achondroplasia is due to the mutations of a gene known as “fibroblast growth factor receptor-3” (FGFR3). The FGFR3 gene is located on the short arm (p) of chromosome 4 (4p16.3). The FGFR3 gene provides instructions for making a protein that is involved in the development and maintenance of bone tissue. Two specific mutations in the FGFR3 gene are responsible for almost all cases of achondroplasia. These mutations cause the FGFR3 protein to be overly active, which interferes with skeletal development and leads to the disturbances in bone growth seen with this disorder.
About 80 percent of the cases are due to new mutations in the FGFR3 gene.
These are random mutations. They have normal sized parents and there is no family history of dwarfism. The remaining cases, have inherited an altered FGFR3 gene from one or two affected parents. Individuals who inherit two altered copies of this gene have a severe form of achondroplasia that causes extreme shortening of the bones and an underdeveloped rib cage. These cases are usually still birth or die soon after birth due to respiratory failure.
When both parents have achondroplasia, 75% of their offspring is affected, of which, 25% are homozygous i.e. they have two copies of the gene (which is ordinarily fatal in the first few months of life), 50% is heterozygous (have only one copy of gene), and 25% are unaffected. When one parent has achondroplasia, the chance of transmitting this gene to each child is 50%.
How common is Achondroplasia?
Achondroplasia appears to affect males and females in equal numbers. All races are affected equally. About 10,000 individuals have achondroplasia in the United States. Worldwide, achondroplasia is the most common skeletal dysplasia, affecting about 1 in every 40,000
children.